Question

Calculate the radius of $He$ atoms if its Vander Waal's constant ${}^{\prime }{b}^{\prime }$ is 24 $mlmo{l}^{-1}$ (Note $ml$ = cubic centimeter).

• A. $1.355\mathring{A}$
• B. $1.314\mathring{A}$
• C. $1.255\mathring{A}$
• D. $0.355\mathring{A}$

Answer 1

The correct option is A $1.355\mathring{A}$

Given, $b=\left[\frac{4}{3}\pi r^3\right]\times 4N$

$24\times {10}^{-3}litres/mol=[\frac{4}{3}\times 3.1416\times r^3]\times 4\times (6.023\times {10}^{23})$

$r^3=2.37\times {10}^{-27}d{m}^3$

$r=1.355\times {10}^{-9}dm=1.355A^o$

Hence, the radius of $He$ atoms is $1.355A^o$